Holistic approach for the design of single piles and pile groups under cyclic loading

桩在轴向和横向循环荷载作用下的长期荷载-位移特性是桩基设计的基础。这种行为的预测与很大的不确定性有关，因为与传统工程结构相比，循环载荷的类型不同，载荷循环次数也极多。需要一种设计方法，能够涵盖循环和高循环荷载下的土壤行为以及桩结构的特定行为。现有的设计方法已经表现出显着的不确定性单调加载。该研究项目的主要目标是进一步开发一种基于现有路基反力法（称为SRMHYP）的设计方法，该方法目前设计用于砂中的横向循环荷载单桩。该模型计划在项目结束时涵盖以下情况：单桩和群桩、砂和粘土、循环和高循环轴向和横向加载、小变形和大变形的土壤刚度、砂的速率无关行为和粘土的速率相关行为、桩安装和设置的影响。该扩展模型将通过离心试验、数值模拟和已有的现场试验结果进行验证。所有计划的实验，模型和数值模拟设计两种不同的模型土壤，即细均匀的硅砂和高岭土粘土代表非粘性和粘性土壤。循环加载的砂和高岭土的实验室试验的结果被用作SRMHYP模型的输入参数，用于进一步开发高岭土的应力-应变模型，用于进一步开发砂和粘土的高循环累积模型，以及用于校准砂和粘土的亚塑性和粘-亚塑性模型。在定义的条件下，在砂土和粘土中的循环加载桩的离心试验的结果被用来验证SRMHYP模型，以及另外的数值模拟，因为测试是在现实的应力水平下进行的。桩在循环荷载和高周反复荷载作用下的数值模拟是基于连续介质法和有限元法。因此，进一步发展的粘土应力-应变模型和砂/粘土的积累模型，上述应用。接触面桩/土的接触模型以及FE程序的用户子程序的额外工作是必要的。数值模拟的结果作为基础的抽象的更简单，更少的计算机消耗SRMHYP模型。利用离心试验和现场试验结果对模拟模型进行了验证。

Long term load-displacement behaviour of piles under cyclic axial and lateral loading is essential for the design of pile foundations. The prediction of this behavior is linked to large uncertainties due to the distinct type of cyclic loading as well as the extremely high numbers of load cycles compared to conventional engineering structures. There is a need of a design approach being able to cover the soil behavior under cyclic and high-cyclic loading and the specific behavior of pile constructions. Existing design approaches show significant uncertainties already for monotonic loading. The major objective of the research project is the further development of a design approach based on an existing subgrade reaction method called SRMHYP, that is currently designed for lateral cyclic loaded single piles in sand. This model is planned to cover the following cases at the end of the project: single piles and pile groups, sand and clay, cyclic and high-cyclic axial and lateral lading, soil stiffness for small and large deformation, rate-independent behavior of sand and rate-dependent behavior of clay, effects due to pile installation and set-up. This extended model will be validated by means of centrifuge tests, numerical simulations, and existing results of field tests. All planned experiments, models and numerical simulations are designed for two different model soils, namely a fine uniform silica sand and a kaolin clay representing non-cohesive and cohesive soils. The results of the laboratory tests on sand and kaolin with cyclic loading are used as input parameters for the SRMHYP model, for further development of a stress-strain model for kaolin, for further development of high-cycle accumulation models for sand and clay, and for calibration of hypoplastic and visco-hypoplastic models for sand and clay. The results of the centrifuge tests on cyclic loaded piles in sand and clay under defined conditions are used to validate the SRMHYP model, and additionally the numerical simulations, because the tests are carried out under a realistic stress level. The numerical simulations of piles under cyclic and high-cyclic loading are based on the continuum approach and the FEM. Therefore, the further developed of the stress-strain model for clay and the accumulation models for sand/clay mentioned above are applied. Additional work on the contact model for the contact surface pile/soil as well as work on the user subroutines for the FE-program are necessary. The results of the numerical simulations serve as a basis for the abstraction of the simpler and less computer consuming SRMHYP model. The simulation models are validated by means of results of centrifuge tests and results from field tests.